The present invention relates to an organic electroluminescent device, a method for manufacturing the device, and an electronic appliance including the device.
An electron-injection layer plays an important role in organic electroluminescent devices (hereinafter referred to as organic EL devices). The luminescent characteristics of organic EL devices greatly depend on the structure of the electron-injection layer. Conventionally, the electron-injection layer is composed of an inorganic material such as lithium fluoride (LiF) and calcium (Ca). Although LiF and Ca are originally insulators, a thin film of LiF or Ca provides an electron-injection effect.
The above materials, however, cannot provide excellent characteristics for all of red (R), green (G), and blue (B) luminescent layers. For example, LiF can provide an excellent electron-injection effect only for B luminescent layers.
To solve the problem, for example, Japanese Unexamined Patent Application Publication No. 2000-243569 proposes an organic EL device including an electron-injection layer composed of an organic metal complex. This complex has a central atom of an alkali metal and a chelating ligand coordinated to the central atom. If such a complex is disposed between an organic luminescent layer and an inorganic cathode, the complex provides high adhesion at both interfaces to enhance the luminescent characteristics of all of R, G, and B luminescent layers. In addition, for example, the above structure can be applied to top-emission organic EL devices to enable a brighter display because a transparent cathode including a metal complex can be readily formed.
The above device, however, cannot provide sufficient luminescent efficiency, and therefore still higher luminescent efficiency is expected. In this device, additionally, the central atom of the complex may be separated from the ligand to diffuse into the luminescent layer as an impurity during the formation of the cathode, thus failing to provide stable characteristics.
An object of the present invention, which aims at solving the above problems, is to provide an organic EL device that can provide an excellent electron-injection effect for all of R, G, and B luminescent layers and that has stable luminescent characteristics, a method for manufacturing the device, and an electronic appliance including the device.